Throat and cone gas injector and gas distribution grid for slurry reactor (LAW646)

ABSTRACT

A gas distribution grid for a slurry reactor includes a plurality of gas injectors horizontally arrayed across, and extending through, an otherwise gas and liquid impervious plate. The injectors have a throat open at both ends, with a gas pressure reducing bore at one end which is the entrance end and with the other end opening into an upward opening cone. Flow diverting means in the injectors prevents slurry solids from entering the throat and being attrited by the high velocity gas jet exiting the bore into the throat. It is preferred that the gas injectors not protrude above the top surface of the grid and flat space is eliminated by means such as angular fillers, to prevent solids accumulation top of the grid. A chamfer may be present at the junction of the bore and throat to prevent unrestricted expansion of the gas jet entering the throat. This is useful for injecting gas into a reactive hydrocarbon synthesis slurry in a slurry reactor, with reduced catalyst attrition and deactivation.

This is a Division of application Ser. No. 08/955,130, filed Oct. 21,1997, now U.S. Pat. No. 6,076,810.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The invention relates to a throat and cone gas injector and a gasdistribution grid containing same. More particularly, the inventionrelates to a throat and cone gas injector and to a gas distribution gridcontaining a plurality of these injectors useful for injecting a gasinto a slurry which contains particulate solids, with reduced solidsattrition and injector plugging.

2. Background of the Invention

There are many applications in which a gas must be injected up into aslurry which comprises particulate solids in a liquid. These includecoal liquefaction, resid refining, other hydrogenation processes, slurryhydrocarbon and oxygenate synthesis, waste water treating, etc. The gasis typically injected up into the slurry by means of a horizontal gasdistribution grid, which is also referred to as a plate or tray, locatedat the bottom of the slurry in a reactor or other vessel, and over a gasspace or cavity called a plenum. The tray contains a plurality of gasinjectors extending therethrough for uniformly distributing the gas upinto the slurry. These gas injectors can be vertical holes in the tray,bubble caps, and the like as is well known. Problems associated withthese trays include solids attrition and plugging of the injectors ifthe gas pressure drops. While solids plugging of the gas injectors isnever desirable, in some applications it is also important to avoidsolids attrition. One specific example is a slurry hydrocarbon synthesis(HCS) process in which a synthesis gas (syngas) comprising a mixture ofH₂ and CO is bubbled up into and through a slurry in a reactor atreaction conditions effective to convert the syngas to hydrocarbons, atleast a portion of which are liquid at the reaction conditions. In thisprocess, the slurry comprises solid catalyst particles and gas bubblesin a hydrocarbon slurry liquid, with the slurry liquid comprising liquidHCS products. Reactors which contain a three phase slurry are sometimesreferred to as slurry “bubble columns”, as is disclosed in U.S. Pat. No.5,348,982. The amount of syngas injected up into the slurry to providethe desired level of hydrocarbon synthesis is typically more than thatneeded to keep the catalyst particles dispersed in the liquid. Problemsencountered with this (and other processes) include plugging of the gasinjectors by the catalyst particles, catalyst particle attrition by thegas which produces fines and results in catalyst loss and plugging unitsdownstream of the reactor, deactivation of catalyst settling on the flatspaces on the tray and catalyst falling down through the injectors intothe plenum space below. It would therefore be an improvement to the artto use gas injecting means which reduce or eliminate any of theseproblems.

SUMMARY OF THE INVENTION

The invention relates to a gas injecting means useful for injecting gasinto a slurry containing particulate solids, with reduced solidsattrition and injector plugging. More particularly the invention relatesto a throat and cone gas injector and to a gas distribution gridcomprising a plurality of the gas injectors horizontally arrayed ordistributed across, and vertically extending through, an otherwise gasand liquid impervious horizontal plate or tray, which will typically belocated at the bottom of the slurry. In one embodiment, all or a portionof the gas injectors are formed as an integral part of the grid. The gasinjector comprises a throat or elongated, hollow, first gas expansionzone open at both ends, with one end being a gas entrance having a borethrough which gas is passed from outside the jet, past an orifice whichis the exit of the bore, and into the throat, with the other, downstreamend opening into an upwardly and outwardly extending second gasexpansion zone, which may be cone-shaped. An internal shoulder at thejunction of the throat and cone provides a flow diverting means, whichdirects slurry seeping down along the wall of the cone radially inwardinto the gas jet exiting the throat, to prevent slurry solids attritionand throat plugging. In a typical injector of the invention, the innerdiameter of this shoulder is substantially the same as that of thethroat and its outer diameter peripherally terminates at the inner wallof the bottom of the cone. It has been found that the absence of theshoulder, or flow diverting means in the gas injector, can result insignificant and substantial disintegration of the particulate solidsinto fine particle sizes by attrition. These fines are carried up andout of the reactor in the overheads, and also pass through liquidfilters into downstream units. This results in a continuous andsubstantial loss of catalyst and also forms sludge in downstream unitswhich can clog the units and which must eventually be separated from theproduct. The pressure drop through the bore is determined by itsdiameter or cross sectional area, which is smaller than that of thethroat. The aspect ratio and diameter of the throat are sized to (i)insure that the expanding gas jet flowing up through the throat contactsthe inner throat wall before it exits the throat and enters the coneand, in combination with the orifice diameter, (ii) achieve the desiredgas velocity in the cone where it contacts the slurry. This wallcontacting in the throat is important to obtain a more uniform velocityprofile of the gas stream entering the cone by allowing the velocity atthe outer periphery of the gas jet to fully develop and to prevent flowperturbations and irregularities at the outer periphery of the jet whichmight otherwise result in solids weeping down into the throat, wherethey will be attrited by the higher velocity gas jet entering the throatthrough the narrow, smaller orifice. The throat has a length to diameterratio (aspect ratio) of less than 10:1 and preferably less than 8:1 toprevent throat plugging by slurry solids. This aspect ratio must also belarge enough for the outer periphery of the expanding gas jet to contactthe inner wall of the throat before exiting it, and preferably make thecontact a finite distance upstream of the throat exit, to provide amargin of safety (e.g., at least 10% of the throat length). It ispreferred that the longitudinal axis of the bore, throat, shoulder andcone all be coincident. The angle of the interior cone wall ispreferably greater than the angle of repose of the slurry solids, toprevent solids build-up in the cone. While in a preferred embodiment,the bore, throat, shoulder and cone all have a circular cross-sectionperpendicular to their longitudinal axis, other cross-sections may beemployed if desired. A plurality of these injectors, verticallyextending through and horizontally arrayed or arranged across ahorizontal, and otherwise gas and liquid impermeable plate or tray atthe bottom of the slurry, uniformly distribute gas up into the slurry,with a fairly uniform pressure drop and concomitant uniform gasinjection velocity across and through each gas injector in the tray.This is determined by the desired gas throughput into the slurry, thenumber of injectors in the tray, the diameter of the injector bore, andthe gas pressure upstream of the injector bore.

Close packing of the injectors across the grid will substantially reducethe amount of flat surface on the top of the grid. In a furtherembodiment, no part of the injector extends up past the top of the gridplate. These two features minimize the amount of dead space on the gridfor slurry solids to settle on. In the case of a slurry hydrocarbonsynthesis (HCS) process in which at least a portion of the solids are anHCS catalyst, the reduced solids settling results in less catalystdeactivation. The gas distribution grid is typically located above thesynthesis gas (syngas) reservoir or plenum area at the bottom of thereactor. The syngas feed is passed into a plenum under the grid whichserves as a pressure damper and which, in combination with the diameterof the orifice in the gas jets, the number of jets and gas pressure,insures that the amount of syngas entering each injector in the grid isthe same.

Gas passing through the pressure reducing bore and into the throat orfirst expansion zone, exits the orifice as a radially outwardlyexpanding gas jet which flows through the throat and contacts the innerwall before it enters the cone. This contact is important, as it resultsin more energy being directed to the outer periphery of the jet exitingfrom the throat and into the cone, or second expansion zone. Thisprovides sufficient gas velocity and mass (energy) at the periphery ofthe jet exiting the throat to prevent slurry from seeping down into thethroat where the solids can be attrited into fines by the relativelyhigh velocity gas jet entering the throat from the bore. It also reducesthe difference in gas velocity between the outer periphery and thecenter of the jet, which further reduces particle attrition when the gascontacts the slurry. As the gas jet exits the throat, it doesn't contactthe inner cone wall at the throat and cone junction, because of theannular shoulder. In one embodiment, the inner periphery of the shoulderis adjacent the inner wall of the throat at its exit and the outerdiameter peripherally terminates at the inner cone wall at the bottom ofthe cone. The shoulder acts as a flow diverter for slurry seeping downthe wall of the cone by imparting a radially inward direction to thedownflowing slurry. Slurry which flows down along the interior cone wallreaches the shoulder, which forces the downcoming slurry radially inwardto where it meets the upflowing, expanding jet exiting the throat, whichcarries weeping the slurry back up into the slurry body above. As theexpanding gas jet travels up through the cone, it contacts the slurryand breaks up into bubbles which have a net upward velocity greater thancan be achieved with bubble caps and the like. In a further embodiment,the orifice opens into a cone or chamfer, or other means (depending onthe shape of the orifice and throat) which prevents unrestrictedexpansion of the gas jet as it enters the throat, thereby preventingback swirls and eddies from forming which can be drawn into theexpanding gas jet and disturb or cause perturbations, such as ripples,and other flow disturbances at the outer jet periphery as it travels upthe throat and into the cone and also cause fluctuations in the jetitself. Such perturbations can permit slurry solids to weep down intothe throat where they are attrited by the incoming higher velocity gasjet. The cone or chamfer thus stabilizes the expanding gas jet and hasalso been found to be beneficial in clearing the throat of solids due toreductions in the gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional schematic of a gas injector of theinvention as an integral part of a gas distribution grid.

FIG. 2 is a variation of the embodiment of FIG. 1.

FIG. 3 briefly illustrates a replaceable orifice assembly for a gasinjector of the invention.

FIG. 4 schematically shows the orifice opening up into a cone or chamferat the bottom of the throat of the gas injector.

FIG. 5(a) illustrates an expanding gas jet exiting the orifice andcontacting the wall of the throat with a free expansion zone proximatethe orifice, while FIG. 5(b) shows the orifice opening out into a coneor chamfer to eliminate the free expansion zone of FIG. 5(a).

FIG. 6 schematically illustrates, in partial cross section, of anotherembodiment of a gas injector and grid of the invention.

FIGS. 7(a) and 7(b) respectively schematically illustrate a side viewand a top plan view of an embodiment of a short cylindrical gasdistribution grid.

FIG. 8 is a perspective of an arcuate, pyramidal spacer for eliminatingflat areas on the top of the grid.

FIG. 9 is a top plan view of a portion of a grid showing the location ofthe pyramidal spacer.

FIG. 10 is a simplified cross-sectional schematic of a slurryhydrocarbon synthesis reactor containing a gas distributing grid of theinvention.

DETAILED DESCRIPTION

Referring to FIG. 1, a gas injector of the invention 10 is illustratedas an integral part of a slurry reactor gas distributor grid 30comprising a horizontal, disk-shaped steel plate 32, shown in partialform, which contains a plurality of gas injectors horizontally arrayedacross the tray and extending vertically therethrough, of which only theone, 10, is shown for the sake of convenience. The top and bottom of thegrid or plate are indicated at 34 and 36. The gas injector 10 extendsvertically through the plate and comprises a cylindrical bore 14 definedby peripheral wall 16 which opens into a throat 20 through an orifice 12which is the upper end of bore 14. The orifice opens up into throat 20by means of shoulder or chamfer 18. While shoulder 18 is shown ashorizontal and flat which means that orifice 12 is a sharp-edgedorifice, in one embodiment it opens upward and outward from theperimeter of the orifice to the inner throat wall 22 as is explainedbelow. In the latter case, the angular opening or chamfer extending fromthe orifice inhibits unrestricted expansion of the gas jet exiting theorifice up into the throat. Throat 20 is a cylindrical bore defined by aperipheral wall 22. Gas passes through bore 14 and emerges out of theupper end of the bore, which is the orifice, into throat 20 as a coneshaped, expanding gas jet which is illustrated in FIG. 5 and explainedin detail below. Passage of the gas through the bore reduces itspressure, so that the gas pressure in the throat is less than thatupstream of the bore (e.g., in the plenum below the grid). The gas jetentering the throat has an included angle ranging from about 10-20degrees and more typically 15-20 degrees, as is known by those skilledin the art. The velocity of the expanding gas jet is reduced as itpasses up through the first expansion zone or throat 20. The aspectratio or length to diameter ratio of throat 20 is sized to permit thedesired velocity reduction of the jet and, at the same time, insure thatthe expanding gas jet contacts the peripheral inner wall 22 of thethroat, before it exits the throat at 24 and enters up into the secondgas expansion zone or cone 30. In general, the aspect ratio will be atleast 2 to insure that the expanding gas jet contacts the wall of thethroat. On the other hand the maximum aspect ratio should not be largerthan 8 or 10, to prevent throat plugging by the slurry solids, in theevent of a reduction in gas flow. In the event of a reduction of theupstream gas pressure or a temporary cessation of the gas flow, theinjector will fill up with the slurry solids and it has been determinedthat an aspect ratio greater than about 8 or 10 can prevent the gas frompushing out the solids when the pressure is restored, thereby pluggingthe injector and rendering it inoperable. It is also preferred that theexpanding gas jet contact the throat wall sufficiently upstream of thethroat exit to provide a factor of safety which can range anywhere fromabout 25% to about 75% of the throat length. As mentioned above, thiscontacting is an essential feature of the gas injector of the inventionto insure sufficient gas velocity proximate the wall 22 at the throatexit 24, to prevent slurry weeping down the side of the cone fromentering the throat. This also results in a more uniform horizontal gasvelocity profile flow across the top or exit 24 of the throat. Throat 20opens into the radially upward and outward extending second gasexpansion zone 30 at the horizontal, circumferential flow divertingmeans illustrated as an annular shoulder 26. Zone 30 is a cone-shaped,and more specifically frusto-conical as defined by the frusto-conicalperipheral wall 28 cut into the upper portion of the tray. In zone 30,the gas velocity is further reduced down to a level where it will notcause catalyst particle attrition, yet still be high enough to suspendthe solids in the slurry and, in the case of a slurry reactor, provide agas flow rate sufficient to achieve the desired reactor output. In thecase of injecting synthesis gas into a slurry hydrocarbon synthesisreactor, the gas flow rate required for efficient hydrocarbon synthesisis typically greater that that required for catalyst suspension. Theexpanding gas jet contacts the slurry in zone 30 and breaks up intobubbles which rise up through the slurry. Slurry weeping down along theinterior of the cone along wall 28 reaches shoulder 26 which imparts aradially inward direction and velocity to it and, as a consequence, theslurry is directed into the gas stream flowing up out of the throat exit24. This lifts the downflowing slurry back up and into the slurry bodyabove, while minimizing seeping of the slurry down into the throat whereit will be attrited. It has been found that the use of the shoulder canresult in as much as a twenty fold reduction in catalyst attrition.While it is believed that the most efficient cross-section of theorifice, throat and cone is circular, it is possible that in some casesone or more of these elements will have a cross-section other thancircular. In the case of a cross-section other than circular, thediameter is taken as the equivalent diameter which is the square root ofthe cross-sectional area divided by pi, and the equivalent diameter isused in determining the aspect ratio of the throat.

FIG. 2 illustrates an embodiment of the invention similar to that ofFIG. 1, but differs in that the bore and throat are a single,cylindrically shaped and externally threaded assembly 40 screwed into amating threaded bore in the tray, indicated by screw threads 58. Thebore 44, bore wall 46, orifice 42, throat 50 and wall 52 are identicalto those shown in FIG. 1. However, the inner portion of the top 54 ofcylinder 40 forms the flow diverting shoulder at the junction of thethroat and cone. Assembly 40 screws up into the tray to where it meetswith annular shoulder 56 at the bottom of the cone. That portion of thetop of the cylinder 40 which does not contact the shoulder 56 forms theannular flow diverting means. Thus, in this embodiment the orifice andthroat assembly are removably or detachably attached to the tray forfacile replacement. Other embodiments will be apparent to those skilledin the art, such as a replaceable orifice assembly briefly illustratedin FIG. 3 and the like. Thus, in FIG. 3, a replaceable orifice assembly58 is screwed up into a mating bore at the bottom of throat 20. FIG. 4illustrates still another embodiment in which the bore 14 of FIG. 1opens up into throat 20 by means of a chamfer or cone shaped wall 15. Inthis embodiment, the expanding gas jet exiting up out of orifice 12 isprevented from freely expanding out to the throat wall 22 proximate tothe orifice 12 as it does in the embodiment of FIG. 3, by the cone orchamfer. This is illustrated in FIGS. 5(a) and 5(b). Thus, in FIGS. 5(a)and 5(b) an expanding, conical gas jet indicated as two wavy lineshaving an included angle α, exits orifice 12 and 12′ and contacts theinner, cylindrical wall 22 of throat 20 at 25. In FIG. 5(a), space 11surrounding the sharp-edged orifice 12 permits free expansion of part ofthe gas jet. Free expansion of the gas jet exiting orifice 12′ isprevented by the cone or chamfer shaped wall 13 in the embodiment ofFIG. 5(b). It has been observed that the presence of a cone or chamferproximate the orifice prevents perturbations in the gas flow at theouter periphery of the expanding gas jet and also enables the gas tomore easily blow out solids that may have filled up the throat during alowering or cessation of the gas pressure upstream of the orifice. Thecone angle should be determined experimentally for each case, but, ingeneral, it will have an included angle less than the angle of repose ofthe solids in the slurry, to prevent slurry solids build-up on theinterior cone wall. Generally, the included angle will be less than 140degrees and in some embodiments, will be less than 90 degrees.

Referring now to FIG. 6, a gas injector of the invention is shown beingsimilar in most respects to that of FIG. 1, except it is not an integralpart of a gas distribution tray. In this embodiment, the gas injector isa separate unit which is attached, by suitable means (e.g., screwthreads) not shown, to a mating bore 72 extending through the tray fromtop to bottom. Thus, turning to FIG. 6, gas injector 60 comprises acylindrical bore 62 which defines orifice 64 at its downstream end.Orifice 64 opens up into a larger diameter cylindrical bore 66 which isthe throat or first expansion zone. Bore 66 opens up into a second,hollow, conical expansion zone 70 by means of annular shoulder 68, whichis the slurry radial flow diverting means. The angle of the cone is lessthan the angle of repose of the solids in the slurry, to prevent solidsaccumulation on the inner cone wall. In this embodiment, even when aplurality of such injectors are horizontally arrayed across the surfaceof the tray, for each injector there will be an annular, flat surface ontop of tray 32 below the cone, indicated at 74 for injector 60. In thecase where the slurry solids comprise catalyst particles whichdeactivate when not in contact with the uprising gas, this space and thearea 76 above 74 bound at the top by the cone is a dead space, in whichcatalyst particles will accumulate and deactivate. Hence, in such casesan embodiment similar to that of FIG. 1 or 2 is preferred, unless othermeans are used to block off the dead space or pass gas through it toprevent catalyst accumulation.

FIGS. 7(a) and 7(b) respectively schematically illustrate a side viewand a top plan view of an embodiment of a short cylindrical gasdistribution grid or tray according to the invention, in which the gridcontains a plurality of gas injectors of the invention horizontallyarrayed across and extending through the grid in a manner similar tothat shown in FIG. 1. However, in this embodiment the grid is formed oftwo separate circular, or disk-shaped plates 82 and 84, assembled andheld together by suitable means such as screws or bolts (not shown).Upper plate 82 of the grid contains a plurality of conical cavities 86extending therethrough which make up the second gas expansion zone foreach injector. Lower plate 84 contains respective concentric matingthroat and orifice cavities, indicated briefly as 88 and 90, extendingthrough it and being coaxial with the longitudinal axis of each cone asshown. The throat diameter is smaller than the bottom of each respectiveand mating conical cavity in the top plate 82, so that the annularshaped flow diverting shoulder 92 is formed when the top and bottomplates are joined to form the completed grid. The top plan view is shownin greater detail in FIGS. 7(b) and 9 explained below. No matter howclose each cone is to its adjoining neighbors, there must be a flatspace on top of the tray between the cones which is indicated as 96 inFIG. 7(b). This space, on which catalyst will settle and deactivate, isreadily reduced and even eliminated by an arcuate, pyramidal spacer 94illustrated in perspective in FIG. 8 and in plan view in FIG. 9. In theembodiment shown, the top of the spacer is slightly flat and suitablemeans, such as a rounded top screw (not shown) is used to fasten thespacer onto the flat spaces. FIG. 9 shows more detail for the spacer andfor the plan view of the injectors.

FIG. 10 is a simple cross-sectional schematic of a slurry HCS reactoruseful in the process of the invention containing a gas distributiongrid of the invention which is that illustrated in FIG. 7. Turning toFIG. 10, there is shown a slurry HCS reactor 100 comprising acylindrical shell 102 containing a slurry 104 within, which is supportedby a gas distribution grid 106 of the invention of the type illustratedin FIG. 7, except that for the sake of simplicity the gas injectors arenot shown in great detail. The grid comprises one or more circular metalplates horizontally disposed over the plenum space 108 which supportsthe slurry above and which contains a plurality of the gas injectorshorizontally arranged across the flat horizontal surface of the grid andextending vertically therethrough. The outer periphery of the grid formsa seal with the inner surface of the reactor. The hollow space or plenum108 under the grid is both a gas reservoir and a damper to smooth outfluctuations in the feed gas pressure. The syngas feed enters thereactor in the plenum space 108 via feed line 107 and is distributed upinto the slurry 104 through the gas injectors extending through thegrid. The small circles represent gas bubbles and the solid circles thecatalyst particles. A filtration means simply illustrated by box 110immersed in the slurry separates the liquid hydrocarbon products of thesynthesis reaction from the catalyst particles, with the liquid beingwithdrawn via line 112 and passed to further processing and upgrading. Aliquids and solids disengaging space 114 in the top of the reactorcollects the gas products of the hydrocarbon synthesis reaction and theunreacted syngas and passes them out of the reactor as tail gas via line116 to further processing and product recovery and upgrading. By way ofan illustrative, but non-limiting example, for a thirty foot diameterreactor, the grid may contain as many as ten thousand gas injectors witha pressure drop of up to about twenty pounds per square inch across eachinjector.

It is understood that various other embodiments and modifications in thepractice of the invention will be apparent to, and can be readily madeby, those skilled in the art without departing from the scope and spiritof the invention described above. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the exactdescription set forth above, but rather that the claims be construed asencompassing all of the features of patentable novelty which reside inthe present invention, including all the features and embodiments whichwould be treated as equivalents thereof by those skilled in the art towhich the invention pertains.

What is claimed is:
 1. A gas injector comprising a pressure reducingzone having gas entrance and exit ends said reducing zone terminating atits exit end in an orifice which opens into an entrance of an elongatedlongitudinal first gas expansion zone, said first gas expansion zonehaving gas entrance and exit ends at opposite ends of its longitudinalaxis, an inner wall and a substantially constant cross-sectional areaperpendicular to said axis, which area is larger than that of saidorifice, said exit end of said first gas expansion zone opening into agas entrance of a second gas expansion zone having gas entrance and exitends at opposite ends of its longitudinal axis, an inner wall and across-sectional area perpendicular to said axis that increases from saidentrance to exit, wherein said second zone entrance has across-sectional area larger than that of said first zone gas exit.
 2. Agas injector according to claim 1 wherein the aspect ratio of said firstzone is greater than 2:1.
 3. A gas injector according to claim 2 whereinsaid pressure reducing zone has a diameter smaller than that of saidfirst expansion zone, and said injector further comprises a flowdiverting means located proximate the junction of said first and secondzones.
 4. A gas injector according to claim 3 wherein said flowdiverting means comprises an annular shelf whose outer periphery isadjacent to the inner wall at said gas entrance of said second expansionzone.
 5. A gas injector according to claim 4 wherein the inner peripheryof said flow diverting means is proximate the inner wall of said firstexpansion zone.
 6. A gas injector according to claim 5 wherein saidpressure reducing zone and first zone are cylindrical.
 7. A gas injectoraccording to claim 6 wherein said pressure reducing zone opens into saidfirst zone by means of a chamfer to prevent unrestricted expansion of agas jet entering said zone from said pressure reducing zone.
 8. A gasinjector according to claim 1 wherein said first gas expansion zonecomprises a longitudinal conduit.
 9. A gas injector according to claim 8wherein said first and second expansion zone longitudinal axes areparallel.
 10. A gas injector according to claim 9 wherein said firstexpansion zone has an aspect ratio of from 2 to
 10. 11. A gas injectoraccording to claim 10 wherein said pressure reducing zone comprises alongitudinal conduit.
 12. A gas injector according to claim 11 whereinthe longitudinal axis of said pressure reducing zone is parallel to thatof said first and second zones.
 13. A gas injector according to claim 12wherein said second expansion zone is substantially cone-shaped andopens outwardly in a downstream direction.
 14. A gas injector accordingto claim 13 wherein said cone has an included angle of from 90 to 140degrees.
 15. A gas injector according to claim 14 wherein said first andsecond expansion zone axes are coincident.
 16. A gas injector accordingto claim 15 wherein the longitudinal axis of said pressure reducing zoneis coincident with said first and second expansion zone axes.
 17. A gasinjector according to claim 16 used to inject said synthesis gas into ahydrocarbon synthesis reactor.
 18. A gas distribution grid comprising aplurality of gas injectors horizontally arrayed across, and extendingthrough, an otherwise gas and liquid impervious tray, said injectorscomprising a pressure reducing zone having gas entrance and exit ends,said reducing zone terminating at its exit end in an orifice which opensinto an entrance of an elongated, longitudinal first gas expansion zone,said first gas expansion zone having gas entrance and exit ends atopposite ends of its longitudinal axis, an inner wall and asubstantially constant cross-sectional area perpendicular to said axis,which area is larger than that of said orifice, said exit end of saidfirst gas expansion zone opening into a gas entrance of a second gasexpansion zone having gas entrance and exit ends at opposite ends of itslongitudinal axis, an inner wall and a cross-sectional areaperpendicular to said axis that increases from said entrance to exit,wherein said second zone entrance has a cross-sectional area larger thanthat of said first zone gas exit.
 19. A grid according to claim 18wherein the aspect ratio of said first zone of said injectors is greaterthan 2:1.
 20. A grid according to claim 19 wherein at least a portion ofeach said gas injector is an integral part of said tray.
 21. A gridaccording to claim 20 wherein said tray comprises a top plate fastenedto a bottom plate and wherein said second zone of each said injector isan integral part of said top plate.
 22. A grid according to claim 21wherein the longitudinal axis of said orifice and said first and secondzones of said injectors are all coaxial.
 23. A grid according to claim22 wherein said second zone does not extend above the top surface ofsaid top plate.
 24. A grid according to claim 23 wherein flat spaceeliminators are present on flat surfaces at the top of said grid.
 25. Agrid according to claim 20 wherein said pressure reducing zone has adiameter smaller than that of said first expansion zone and saidinjector further comprises a flow diverting means located proximate thejunction of said first and second zones for imparting a radially inwardflow direction to liquid flowing from said second zone towards saidfirst zone.
 26. A grid according to claim 25 wherein said flow divertingmeans comprises an annular shelf whose outer periphery is adjacent theinner wall at said gas entrance of said second expansion zone.
 27. Agrid according to claim 18 wherein the inner periphery of said flowdiverting means is proximate the inner periphery of said first expansionzone.
 28. A grid according to claim 27 wherein said pressure reducingzone and first zone are cylindrical.
 29. A grid according to claim 28wherein said second zone is frusto-conical, with its smaller endproximate the junction between said zones.
 30. A grid according to claim29 wherein said pressure reducing zone opens into said first zone bymeans of a chamfer to prevent unrestricted expansion of a gas jetentering said zone from said pressure reducing zone.
 31. A gridaccording to claim 30 wherein said injectors do not protrude above thetop of said plate.